The present invention relates to an emergency notification and rescue request system for transmitting a rescue request message to predesignated call receiving parties via telephone line when a situation requiring a rescue effort arises. Particularly, the present invention relates to an emergency notification and rescue request system which is suitable for use in households including blind, handicapped, ill or otherwise infirm members.
Households including infirm members may need to call for help to rescue teams and neighbors in case of an accident or a sudden worsening of a sickness. Such household members may not be able to call for help by their own efforts.
In order to solve such a problem, the co-pending U.S. patent application Ser. No. 09/745,975 has proposed an emergency notification and rescue request system for, in response to various emergency situations, automatically dialing one or a plurality of call receiving parties designated to each emergency situation to thereby notify the occurrence of the emergency situation and request rescue efforts. This system comprises a memory capable of storing a plurality of rescue request messages and can assign one or more of the plurality of rescue request messages to each of the combinations of call receiving parties and emergency situations (or corresponding input terminals) so that it is possible to easily conduct emergency notification and rescue request operations with an optimum message depending on a particular combination of emergency situations and call receiving parties.
In such an emergency notification and rescue request system, it is important to transmit the rescue request messages after it is detected that the call receiving party has answered the call. Typically, such detection of the call receiving party""s answer to the call is done by detecting reversal in voltage polarity of the telephone line. However, in the case that a private line is used by the call receiving party as by the fire station, the line polarity reversal may not occur when the call is answered, and this makes it impossible to detect the answer to the telephone call based on the line voltage polarity.
The U.S. Pat. No. 4,492,820 issued to Kennard, et al. has disclosed a telephone alarm device that can detect the call receiving party""s answer to the call even when the line polarity change may not take place. This device comprises a level detector for detecting the presence or absence of audio signals on the telephone line and outputting a signal indicating the presence or absence of the audio signals on the line, a CPU for storing the length of each audio signal in a RAM according to the signal from the level detector, and a ROM for storing time standards. The CPU compares the length of the audio signals with the time standards, and according to the comparison, determines whether the audio signal received is a busy signal, a telephone ring signal or an xe2x80x9codd countxe2x80x9d signal. When a predetermined number of the odd count signals are identified, it is determined that the call has been answered by the call receiving party.
In this telephone alarm device, in order to identify the audio signal as the busy signal, ring signal or xe2x80x9codd countxe2x80x9d signal, it is necessary to prepare beforehand special data such as the xe2x80x9ctime standards.xe2x80x9d However, the length (or duty cycle) and/or period of the ring signal, for example, can vary depending on a switching system (or switching center) relating to a particular call, and thus, different xe2x80x9ctime standardsxe2x80x9d may be required for different switching systems. When appropriate time standards are not set, the answer detection by the telephone alarm device may not properly function.
In view of such problems of the prior art, a primary object of the present invention is to provide an emergency notification and rescue request system having a versatile answer detecting function that can reliably detect an answer to a call even in the case that the ring signal can vary for each call and the line polarity change may not take place when the call is answered.
A second object of the present invention is to provide an emergency notification and rescue request system having an answer detecting function that can detect an answer to a call without requiring special data even when the line polarity change may not take place when the call is answered.
According to the present invention, such objects can be accomplished by providing an emergency notification and rescue request system, comprising: one or a plurality of input terminals for receiving signals from one or a plurality of sensors or from a transmitter operable by a user; an automatic telephone dialer capable of selectively making a telephone call to a plurality of call receiving parties; a memory for storing one or a plurality of rescue request messages; and an answer detector for detecting an answer by a call receiving party to which a telephone call was made, wherein in response to a signal input to any one of the plurality of input terminals, the system makes a telephone call to one or more call receiving parties set for the input terminal and when detecting an answer from the call receiving party, the system transmits one or more rescue request messages assigned to the call receiving party, and wherein the answer detector comprises: a level detector for outputting a first signal when a level of an audio signal on a telephone line is greater than a prescribed level and otherwise outputting a second signal which is different from the first signal; means for computing, in response to a prescribed state change in the output signal from the level detector, an interval between a current prescribed signal state change and a previous prescribed signal state change; a counter for indicating a number of consecutive events that a current interval computed by the computing means does not substantially correspond to a previous interval computed by the computing means; and means for determining that the call receiving party has answered the telephone call when the number indicated by the counter is equal to a prescribed value. The prescribed change in the output signal from the level detector may be a change from the first signal to the second signal or from the second signal to the first signal.
Thus, in this system, an interval between adjacent prescribed state changes in the output signal from the level detector is computed every time the prescribed state change is detected, and the current and previous intervals are compared so that if such an event that the current and previous intervals do not substantially correspond to each other has occurred prescribed times consecutively, it is determined that no regular signals such as the busy signal or ring signal exist on the telephone line, i.e., the call receiving party has answered the telephone call. Therefore, even when the busy signal and/or ring signal may vary depending on the switching systems, so long as the signals are regular (or periodic), it is possible to detect the call receiving party""s answer to the telephone call without need for preparing the special data. Such an answer detection does not rely upon the polarity reversal of the line voltage, and thus, even in the case that a private line is used by the call receiving party as by the fire station, for example, and the line polarity reversal may not take place, the answer to the telephone call can be detected. Thus, it is ensured that the rescue request messages are transmitted after the call receiving party has answered the call, thereby allowing for reliable and effective information delivery and contributing to quick start of rescue efforts.
The above emergency notification and rescue request system may further comprise additional means for determining that the call receiving party has answered the telephone call when the level detector has continuously outputted the first signal for a prescribed period of time.
According to another aspect of the present invention, there is provided a method for notifying an emergency and requesting rescue, comprising the steps of: in response to a prescribed input signal, making a telephone call to one or more call receiving parties assigned to the input signal; detecting that the call receiving party has answered the telephone call; transmitting one or more rescue request messages assigned to the call receiving party when the step of detecting indicates that the call receiving party has answered the telephone call; wherein the step of detecting comprises the steps of: monitoring an output signal from a level detector that outputs a first signal when a level of an audio signal on a telephone line is greater than a prescribed level and otherwise outputs a second signal which is different from the first signal; computing, in response to a prescribed state change in the output signal from the level detector, an interval between a current prescribed signal state change and a previous prescribed signal state change; counting a number of consecutive events that a current interval computed by the computing means does not substantially correspond to a previous interval computed by the computing means; and determining that the call receiving party has answered the telephone call when the counted number is equal to a prescribed value.
Other and further objects, features and advantages of the invention will appear more fully from the following description.